VLCLibrary: do not retain libvlc instance after creation

libvlc_new creates an instance with a ref count of 1 which is sufficient here

Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

Sources/VLCLibrary.m

@@ -94,8 +94,6 @@ static VLCLibrary * sharedLibrary = nil;
         paramNum++;
     }
     _instance = libvlc_new(count, lib_vlc_params);
-    if (_instance)
-        libvlc_retain(_instance);
 
     NSAssert(_instance, @"libvlc failed to initialize");
 }